I used to have 4 days and just keep going through them. Sometimes I'd take a day off. I got to experience different amounts of neglect. It seems doing an exercise once a week was difficult for me to stay at the same weight level. I could stay about the same if I did an exercise once on day 1 and then day 6. I think was going for a 3 day set up, but it kept spilling over into 4 days, because deadlifts and squats are brutal. I ended up deciding to go with time efficiency rather than what might be the optimal workout. For that I recommend combining two unrelated exercises such as bench presses and calf raises. When you rest from one, do the other. They also need to be near each other in your gym. You can also do tops and bottoms such as biceps and triceps or hamstrings and quads at the same time.